1. Field of the Invention
The present invention relates to an image processing apparatus in which a character portion of an image represented by inputted image data has an improved resolution and a picture portion thereof has an improved halftone characteristic.
2. Discussion of the Background
On almost all occasions, only one of either a resolution of an image or a halftone characteristic of an image is improved in conventional image processing apparatus. However, in a case that a character portion and a picture portion mixedly exist in the image, the image quality of either one of both areas is sacrificed (deteriorated).
Furthermore, in a method of performing image area separation, the construction of the image processing apparatus becomes rather complicated and manufacturing costs thereof turn out to be high-cost.
Japanese Laid-open Patent Publication No. 01-52 137378/1989 proposes an image processing system which separates a character image and a photograph image both on a manuscript document, executes separately a filtering treatment to the respective images, performs individually different binarizing processes respectively fitted to the characteristics of the character image and the photograph image, and thereby obtains image data representing clearly both of the character image and the photograph image, respectively.
On the other hand, Japanese Laid-Open Patent Publication No. 02-34233/1990 proposes a detection system for detecting a net-points area in order to separate the character area and the photograph area on a manuscript document.
In such a situation, it is required to provide an image forming apparatus capable of reproducing the resolution and halftone characteristics fitted to the area by use of a low-cost method.
In accordance with the type and the quality of the manuscript document, the image processing functions required to the copying machine differ from each other. In recent years, a copying quality which satisfies the requirements for all items employed as the manuscript document to be copied has been required. At present, there are proposed various types of image processing systems capable of covering almost all of the general manuscript documents. The words of "almost all of the documents" signify primarily manuscript documents constructed with a mixture of character, photograph, etc. just like a magazine or the like, including other documents such as newspapers, documents processed by a word processor, hand-written documents, and so on. In particular, there have been proposed various types of systems capable of covering almost all of the general manuscript documents by aiming at the employment of both of the character and the photograph.
one example of those proposals is described in the specification of the afore-mentioned Japanese Laid-Open Patent Publication No. 01-137378/1989.
However, in the conventional digital copying machine, a copy mode for the character image turns out to be the primary mode (the initial state being in this mode) from the viewpoint that almost all of the manuscripts are character documents. And further, when an operator performs a key operation, the operation of the copying machine can be changed to the mode for the manuscript document in the state of the character-and-photograph mixture image, or to the mode for the photograph image only. The above matters may be due to the idea that the character manuscript is the first leading (primary) part of the general manuscript, and due to the troublesome facts that the treatment of employing both of the character and the photograph is incomplete, a mistake of processing the image area separation occurs, and further, a faint character manuscript cannot be reproduced clearly.
Conventionally, in the digital image processing, there existed two types of image processings; those are, a first processing of putting an emphasis on a resolution for processing a character image, line image, etc., and another processing of putting an emphasis on a halftone for processing a photograph image or other halftone-based image. On this occasion, the characteristics of the image processing method in the former case completely differ from that in the latter case. Therefore, it is necessary to prepare separately an image processing mode for a character or line image and another image processing mode, on many occasions. On the other hand, a character/photograph compatibility mode may discriminate the characteristics of the prepared two image processing modes from the information on the manuscript document and exert preferable treatment, respectively, on both of the above-mentioned modes, on some other occasions.
Regarding the character/photograph areas separation processing method and the character/photograph compatibility processing method, many methods have been proposed in recent years. However, in the former case, it is difficult to completely separate the image area. And further, in the latter case, when both of the character image and the photograph image are processed with the compatibility, the character image quality in the case of specially processing the character image does not turn out to be equal to the photograph image quality in the case of specially processing the photograph image. Therefore, it is a limited improvement method to propose still another mode as the third mode following the first mode specialized in the character image and the second mode specialized in the photograph image.
Furthermore, the object of executing the treatment of separating both of the image areas is to intend to realize the compatibility by preventing the phenomenon of "moire" from occurring for the third mode of the net-points manuscript document on some occasions, contrary to the above-mentioned standpoint of putting the emphasis on the resolution in the case of processing the character image and putting the emphasis on the halftone in the case of processing the photograph image.